But this morning, I was flummoxed until I had a "smack your forehead and say DUH" moment.
In normal commercial construction, squaring and leveling is pretty easy. The site is already leveled out reasonably before the footings are poured and then the framing crew (me) comes in. As you lay out and nail beams and joists and such, you naturally check here and there to make sure everything is 1) square and 2) level, but if your dimensional lumber is straight and cut square at the ends, etc., it's not complicated or difficult to get it right and correct it if something comes up.
I seemed to be getting weird variances of level-ness internal to the decking for the tent, which I've got about halfway laid out and covered, and it took me a little bit to figure out that:
USED PALLETS ARE NEITHER NECESSARILY SQUARE NOR NECESSARILY INTERNALLY LEVEL
Smack forehead. Duh!
The "square" part isn't much of a problem. I just butt the sheets of plywood against each other tightly, make sure the edges match, and I'm good to go.
But for the "level" part, I'm not nailing that stuff down to 2 x 6 joists that I've already leveled. I'm nailing it down to pallets of varying age and varying wear, some of which may have chunks gouged out of their stringers, on which one deckboard might be slightly thicker or thinner than the others, etc. Even if I level each pallet individually, a pallet that's level at the center may be 1/8" higher at one end, etc.
I'm doing a certain amount of shimming, tearing rogue slats off, etc., but ultimately the deck is going to be slightly off-level in various places. The only way I'll be able to correct that is internally -- different numbers of layers of rug, adjusting desk legs, etc.
Which is fine. Using discarded pallets and a plywood cover is saving me somewhere around $1,000 in material costs and doesn't entail TOO much extra labor. Since I only expect the deck and tent to remain usable for 3-5 years, I'd rather have the money than a beautiful deck that would have to be repurposed or torn down when I move on to the next "home office outside the main house" experiment.